A week ago, before the week that was, we were swilling in surrogate memoirs. Tony's troubles with Gordon: Mo's troubles with Tony: Gordon's troubles with everyone. Palpitating stuff - but not the real thing, nothing to match trouble on the forecourt or (eureka!) a Tory lead at the polls. Pause, though, for the memoir mills have not fallen silent. They still grind on, a vital commentary on current debacle.

Andrew Rawnsley is a tried and tested name to Guardian and Observer readers. He's a serious journalist with serious sources. When he writes about Gordon sitting in a minibus listening to one of Tony's big speeches on the radio and heckling away ("The New Deal is up and running." Grunt. "He didn't want that.") he oozes credibility. The relationship between PM and chancellor may be more complex than any single book can chart; that's the way with stormy marriages of mind and ambition. But you don't need to see the whole truth to see enough of the truth. This is a partnership which may, originally, have constructed the electoral phenomenon called New Labour. Now it's a liability.

We know - from the pages of Rawnsley - who stitched up who over Europe, who sacked whose mates, who fiddled while Mandelson burned, and danced around the bonfire. We know about love and hate. What we don't know (exactly) is who briefed and counter-briefed Andrew so commodiously - and why. Nor, perhaps more pressingly, do we quite know what our heroes are saying about each other in private this morning.

"Someone who has an extremely good claim to know the mind of the prime minister", you may recall, once caused a bit of a stink when he talked to Rawnsley about Mr Brown's "psychological flaws". But do you remember what that someone went on to say? "If you go through the real disasters of our time in government - EMU, the Geoffrey Robinson affair, ISAs, single parents - I'm afraid they all have a single thread to them: they are coming out of the Treasury." An old list in need of updating. Add 75p pension rises. Add the price of petrol at the pumps - in neon lights.

Mr Blair has endured a wretched few days, caught short at a Chinese supper in Humberside all unawares of the tumult around him. Did he make a good fist of the crisis? Not according to some astronomically awful opinion poll verdicts. The first 48 hours of the fire were more flailing than fighting. Stephen Byers and John Reid were fed to the flames bearing notably blue touchpaper and notably duff arguments. But in the end the prime minister found his bearings and dug in on a principle which needed to be sustained. In the end he showed the resolve of leadership, gambling and battling through.

Where, though, was the man who would be leader through this travail? The chancellor didn't exactly put himself about, merely reiterating the impossibility of disturbing the sanctity of the Budget process a couple of times. When the going got tough, he didn't get going. Blair ran cover for Brown. What would "someone with an extremely good claim" make of that?

In a well-ordered world, of course, there would be no cause for recrimination. Policies - including petrol pricing - would have been exhaustively debated around the cabinet table, sealed by collective responsibility. But is that quite the way this chancellor works? Hardly: and the original fallout over the euro is worth invoking here. Mr Blair was anxious not to rule out joining in the first term because that was his political judgment. Mr Brown sought unilaterally to sweep such possibilities from the table because that was his economic judgment. Politics: economics. Thus the cake of governance is carved between the two master chefs. Yet it's a totally unreal division.

The 75p pension rise was economics to a set formula. Low inflation equals a few coins in your pocket. Don't load on extra largesse because we're trying - perfectly sentiently - to lower dependence on the state pension anyway. But politically it was utterly crass, achieving the precise reverse of sentient policy.

And if that's true for pensions, consider the still more awful debacle of the fuel escalator. The chancellor apparently addressed that in his last Budget when he suspended the escalator. Oh no he didn't! Many things - including Opec meetings - happen between Budgets. And they have instant political impact, demanding instant thought. If the ultimate case is green, it has to be made. If it doesn't stick, it has to be made again and again. Politics and economics don't come in separate boxes. They're inextricably mixed.

Here, beyond personalities, is the fundamental point needing fundamental action. Briefing ministers were out and about yesterday, dumping on Gordon (who has no great gift for making friends and influencing people). If there's an immediate scapegoat for this shambles, his name is Brown - and there'll doubtless be a deal of pressure on Mr Blair to exact the penalties of blame. Pressure that a weakened prime minister will have to resist, of course. More flailing in the marsh.

But the real problem goes deeper than petty jealousies and old scores repaid. It is structural - in the division of the 1997 spoils and the spheres of influence. Chancellors of the exchequer are very important chaps, but they aren't islands unto themselves. They have to be part of the team, the political team. They have to share and consult and bear joint responsibility - to keep their minds, in short, on all of the job. When, structurally, that isn't the case, then disaster follows automatically.

Time to take stock. The febrile polls will blow away. William Hague isn't the tiger in anyone's tank. You'd still bet on continuing Labour government (though not, maybe, on a spring election). But one political thing, I think, has changed for good. Gordon Brown will not - in his dreams or in reality - succeed Tony Blair in some genteel pass-the-parcel of power. The aura of invincibility has dropped from him. Look elsewhere for Labour's next leader. The central alliance is bust.

That, surely, must prove a blessing in disguise. There's no more crucial relationship in government than the one between No 10 and No 11. When it fractures -see Lawson and Mrs T - everything falls apart. Even if the petrol gaffe hadn't happened, the euro referendum was geared for inevitable desuetude.

Only Blair - the politician - can repair Labour's damaged fortunes. Everything hangs on him, because there is no alternative. Mr Brown can help for a while en poste, then survive in due course by moving on to the foreign office or some more peripheral role. Structure matters. It has been the rot inside New Labour thus far. The lesson of the longest week is that it has to be got right now - or else.